1. Field of the Invent-on
The present invention relates to a rectilinear motion rolling guide unit in which rollers or balls are used as rolling elements for a linear motion rolling guide unit, and both of a track rail and a slide unit which rides over the track rail are rectilinearly guided and moved by the rolling friction.
2. Description of Related Background Art
Conventional similar guide units have been disclosed in Japanese Patent Application No. 57-181431 (Japanese Patent Application Laid-Open No. 59-73623), Japanese Utility Model Application No. 56-128133 (Japanese Utility Model Application Laid-Open No. 58-33821), and Japanese Patent Application No. 61-46666 (U.S. Pat. No. 4,692,037), respectively.
In the invention of Japanese Patent Application No. 57-181431, particularly, in FIG. 5, there is shown a rectilinear motion rolling guide unit having four tracks of the parallel type in which four corners of a block having a rectangular cross section are chamfered and the chamfered portions are used as track surfaces of rollers (the type in which the rollers are arranged so that the axial centers of the rollers in the load track surfaces are parallel). According to such a type of guide unit, although the load capacities are equal for the loads in the vertical direction, in most of the cases, the downward load is larger than the upward load in the actual use, so that such a structure does not satisfy the practical use condition with respect to the load capacities.
In the invention of Japanese Utility Model Application No. 56-128133, particularly, in FIG. 6, there is shown a guide unit in which a drawback of the high costs which is caused when all of the rolling elements on four tracks use rollers is improved and the upward load is applied by using cheap balls. However, since the track members for the rollers and balls are formed separately from the casing, when they are assembled as a unit, there are drawbacks such that accumulation assembly errors are easily caused and the rectilinear motion rolling accuracy is low. On the other hand, since the number of parts increases, the costs also rise and such a structure is undesirable. Further, according to such a type of guide unit, since the upper surface of the track rail is used as a track surface for the rollers and the endless circulating passageway in the loadless region is also formed at a top position, a cross sectional height of the slide unit is also large.
In the invention of Japanese Patent Application No. 61-46666, the cross sectional height of the whole unit is further lowered than that in Japanese Patent Application No. 57-181431, the axial centers of the rollers are gradually twisted in the loadless circulating passageway near the track surface until the axial centers are set to be vertical, the rollers are smoothly moved on the other endless circulating passageways, and no circulating passageway is formed in the height direction of the unit. However, even in such an invention, there is a drawback such that the unit is expensive because rollers are used as the rolling elements on all of the four tracks.